Noise generator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Noise generator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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There are special devices that allow you to listen to conversations through window panes at a distance. In this case, the property of sound waves is used to create microvibration of glass, which can be converted into sound with the help of narrowly focused optical devices.

To prevent listening to business conversations through the windows allows the broadband acoustic noise generator (Fig. 3.40).

Noise generator
Fig. 3.40

The device is assembled on three CMOS chips and consists of a master oscillator at a frequency of 50 kHz (D1.1, D1.2), a generator of a pseudo-random pulse sequence on shift registers (D2, D3) and logic (D1.3, D1.4).

Sound emitters (HF1, HF2) are VP-1 or DEM-4M capsules used in some phones.

Resistor R4 allows you to adjust the volume of the sound.

The circuit can be powered by any unregulated source with a voltage of 4 to 15 V and consumes no more than 20 mA.

Any small-sized speakers (with 50 ohm impedance) are also suitable as a sound source, but the current consumption will increase. Transistors can be replaced with KT829A.

When properly assembled, the configuration circuit does not require.

The device is made in the form of a portable box and is placed on the windowsill, close to the glass. You can turn on the noise generator during business negotiations, if necessary.

Publication: cxem.net

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